Preparation of gas-expanded plastic materials



Patented May 27, 1952 PREPARATION OF GAS-EXPANDED- PLASTIC" MATERIALSRutl1;..L.. stander, .Washington; D.-.C.,.assigpo1:,to;

United; States Rubber Company,. New,York, N'JYga corporation of. NewJersey Not Drawing-1. Application June 22,1950; S.er.ial ..No. 169,784..

47Claims. (Cl. 2602.5)'

This invention relatesnito thepreparationof.

gasrexpanded plastic materials, particularly to the.T preparation of.closed-cell cellular rubberwith new organic chemical. blowing, agentsadaptede-on thermal decomposition, to yield nitrogen gas. Although thechemicals are primarily adapted to the production of closed-cellcellular rubber, they may also be used in the preparation of cellularrubber in which the cells are. interconnecting as in so-called spongerubber.

Although. there. aremany chemicals that can.

becausedto liberate. nitrogengas for gas -expandingzplastic. materialscapableofibeing set or. cured, such as rubber, many of them lackotherdesirable. attributes. that are necessary for commerciaLuse, namely,little, or. no toxicity, nondiscoloring, or nonrstainingcharacteristics, low cost, ease. of. incorporation, and. preparation,etc.

Accordingly,.it is an.0bject of this invention.

to. provide anew class of efficientnitrogen-gas blowing agents which.have many' of. the. above desired. characteristics and whoseusetherefore.

constitutes an improvement in thisart. Other objects will beapparentfrom the hereinafter description:

The present chemical blowing agents. arecharacterized: by the groupingof. RNH:NH.CB/s.

WhereRand R each represent an aromatic radical, preferably of thebenzene series.

The chemicals may be prepared by condensat ing a. triarylchloromethaneand an aryl hydra.- zine, as illustrated by the equation:

Suitable aryl hydrazo triaryl methanes include: p-chlorophenyl hydrazotriphenyl methane- M. P. 148-9 C. (dec.) Wieland et a1. Berichte 55,1816 (1922); phenylhydrazo-tri-p-anisyl methane-M. P. 154 C. (dec.)Wieland et al. Berichte 55, 1816 (1922); p-tolyl hydrazo triphenylmethane-M. P; 157 C. (dec.) Gomberg and CampbellJ. A. C. S. 20, 780(1898) o-nitrophenyl' hydrazo triphenyl methane-M. P. 168 C. (dec.)Gomberg and Campbell-J. A. C. S. 20, 780 (1898)";m-chlorophenylhydrazotriphenyl methaneM. P. 150 C. (dec.) Gomberg andCampbell-J. A. C. S. 20,780 (189.8) and, phenyl hydrazo.triphenyl.methane,-M. P. 135 C. (dec.) Gomberg. Berichte 30, 2045(1897).

The chemicals can be easily and completely mixed with the rubber orother organoplastic and do not impart an objectionable odor or color.They are, furthermore, non-staining to fabrics and coatings which maycome in contact with therubberi or. other organoplastic. They-:areralsqnonetoxic.

The amount of the chemical, when .used. asthfii sole blowing agentshould exceed 1% and range, up to 20%, or higher, by weight, based on,the content of rubber or other organoplastiedepend ing upon the typeofarticle being produced. However, as little as 0.1% may-be used in corn:junction with otherblowing agents to. obtain val-, uable effects. Inthe. case of plastics other than. natural or synthetic rubbers, the.quantity 01 blowing agent may range as high as:30 0r..mbre parts,.byweight, per 10.0v parts of. thegplastic The following examples are giventoillustrate the invention; parts being by weight:

A. rubber master, batch was made. upby; come: bining the-followingingredients, on ,a rubber.- in the. usual manner;

Pheny1 hydrazo triphenyl methane 3.0"

The. rubber stocks. were. sheeted into. A; i sheets; anddiscs 2%indiameter were ..cut,.each.weigh=. ing about grams. These were placedin clrp cular molds measuring deepand. 3" indiameter. The samples werethenpress cured, for 20 minutes at the temperature of pounds.- steam?pressure. Upon removal from the molds eachof. the samples wasobtainedasa well-formed sponge: disc, exhibitin a fine and uniformcellular.struc.- ture.

Portions of the stock, after coatingwith.- white.- nitrocelluloselacquer and then driedrand exposed: to. sunlight (5v days), showedlittle or nodiscolora ation. The compoundedrubber wasalsoinonstainingto: cloth;

With therubber may; be. incorporated the usual; compounding ingredients,including; curing-, or; vulcanizing agents. such as sulfur,-accelerators;;. activators, antioxidants, plasticizers, softeners,pigments, fillers, dyestufis, etc. If desired, reclaimed rubber may beincorporated in the mix. The rubber may be first broken down on the millwhereupon the blowing agent may be added followed by other ingredients,curatives usually 3 i being added last. After compounding, I prefer toallow the stock to stand for a day or more before carrying out theblowing and curin step or steps.

The manipulative methods of treating the compounded stock to obtain theexpanded prodnot are those which are well-known and standard in the art.For details of the art of making chemically gas-expanded plastics suchas rubber, attention may be directed to the article Cellular Rubbers byGould appearing in Rubber Chemistry and Technology, vol. 17, pp. 943-956(October, 1944), and U. S. Patents to Cuthbertson No. 2,291,213 and toRoberts et al. No. 2,299,593. It is well within the present skill of theart, in the light of this disclosure, to compound a stock containing myblowing agent and process it so as to obtain either a sponge or a closedcell type of product.

The decomposition temperatures for gas-expanding by means of thechemical blowing agents may range from 80 C. to 200 C. Accordingly, theorganoplastic should be capable of setting to a normally solid state andhave suiiicient consistency and tensile strength at temperatures of fromabout 80 C. to about 200 C. to retain the expanded structure resultingfrom the subsequent heating step involving decomposition of the blowingagent with evolution of nitrogen and expansion of the mass either in themold or when removed therefrom.

It is not intended to confine the invention to gas-expanding naturalrubber, since it can be applied to other organoplastics, and mixesthereof, such as are shown in U. S. Patent No. 2,448,154:, namely, alkydresins, urea-formaldehyde resins, polymerized unsaturated materials suchas polyacrylonitrile, polystyrene, polyvinyl chloride, copolymers ofvinyl chloride and vinyl acetate, amorphous non-resinous plasticmaterials such as cellulose esters, cellulose ethers, synthetic rubberssuch as the rubbery copolymers of butadiene and styrene oracrylonitrile, rubbery copolymers of isobutylene and butadiene orisoprene polychloroprene, polyisobutylene, olefin polysulfides, etc. Thepreferred aspect of the invention is concerned with chemically blowncellular rubber because of its wider commercial advantages, incopetition with foamed rubber latex products.

The organoplastic may be of either the thermoplastic or thethermosetting type and it may be of a type of which polymerization isfurthered or completed during the step of heating to generate the gas.

The invention is especially applicable to the expansion of rubber, Anytype of rubber which is curable or vulcanizable to a solid state may beemployed, examples being natural rubber or synthetic rubber-like orrubbery materials such as rubbery copolymers of an aliphatic conjugateddiolefin such as butadiene or isoprene with a copolymerizable materialsuch as styrene or acrylonitrile rubbery copolymers of olefins and diolefins such as that known in the art as butyl rubber which is thecopolymer of isobutylene with a small proportion of an aliphaticconjugated diolefin such as butadiene or isoprene, polymerizedhalo-diolefins such as polymerized 2-chloro-1,3- butadiene, polymerizedolefins such as polyisobutylene, polymeric organic sulfides such asolefin polysulfides, etc.

Having thus described my invention, what I claim and desire to protectby Letters Patent is:

1. The method of making a gas-expanded 0rganoplastic material whichcomprises mixing an aryl hydrazo triarylmethane of the formulaR-NH-NH-CR/a, where R is selected from the class consisting of arylhydrocarbon, nitro-substituted aryl hydrocarbon, and chlor-substitutedaryl hydrocarbon radicals, and R is selected from the class consistingof aryl hydrocarbon and alkoxy-substituted aryl hydrocarbon radicals,with an organoplastic material which is capable of setting to a normallysolid state and havi sufiicient consistency and tensile strength attemperatures of from C. to 200 C. to retain the expanded structureresulting from the subsequent heating step, and decomposing saidtriarylmethane by heat to evolve nitrogen and expand said organoplasticmaterial.

2. The method of making a gas-expanded rubber which comprises mixing anaryl hydrazo triarylmethane of the formula RNH-NH--CR':, where R isselected from the class consisting of aryl hydrocarbon,nitro-substituted aryl hydrocarbon, and chlor-substituted arylhydrocarbon radicals, and R. is selected from the class consisting ofaryl hydrocarbon and alkoxy-substituted aryl hydrocarbon radicals, withthe rubber, decomposing said triarylmethane by heat to evolve nitrogenand expand said rubber, and curing the rubber to cause it to retain itsexpanded condition,

3. The method of making a gas-expanded organoplastic material whichcomprises mixing an aryl hydrazo triarylmethane of the formulaR,NII-NHCR'3, where R is selected from the class consisting of arylhydrocarbon, nitro-substituted aryl hydrocarbon, and chlor-substitutedaryl hydrocarbon radicals, and R, is selected from the class consistingof aryl hydrocarbon and alkoxy-substituted aryl hydrocarbon radicals,with an organoplastic material which is capable of setting to a normallysolid state and having sufficient consistency and tensile strength attemperatures of from 80 C. to 200 C. to retain the expanded structureresulting from the subsequent heating step, decomposing saidtriarylinethane by heat to evolve nitrogen and expand said organoplasticmaterial, and causing said organoplastic material to set and retain itsexpanded condition.

4. The method of making a gas-expanded rubber which comprises mixingphenyl hydrazo triphenylmethane with the rubber, decomposing saidtriphenylmethane by heat to evolve nitrogen and expand said rubber, andcuring the rubber to cause it to retain its expanded condition,

RUTH L. STANDER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,990,925 Bennett Feb. 12, 19352,448,154 Richmond et a1 Aug. 31, 1948

1. THE METHOD OF MAKING A GAS-EXPANDED ORGANOPLASTIC MATERIAL WHICHCOMPRISES MIXING AN ARYL HYDRAZO TRIARYLMETHANE OF THE FORMULAR-NH.NH-CR''3, WHERE R IS SELECTED FROM THE CLASS CONSISTING OF ARYLHYDROCARBON, NITRO-SUBSTITUTED ARYL HYDROCARBON, AND CHLOR-SUBSTITUTEDARYL HYDROCARBON RADICALS, AND R'' IS SELECTED FROM THE CLASS CONSISTINGOF ARYL HYDROCARBON AND ALKOXY-SUBSTITUTED ARYL HYDROCARBON RADICALS,WITH AN ORGANOPLASTIC MATERIAL WHICH IS CAPABLE OF SETTING TO A NORMALLYSOLID STATE AND HAVING SUFFICIENT CONSISTENCY AND TENSILE STRENGTH ATTEMPERATURES OF FROM 80* C. TO 200* C. TO RETAIN THE EXPANDED STRUCTURERESULTING FROM THE SUBSEQUENT HEATING STEP, AND DECOMPOSING SAIDTRIARYLMETHANE BY HEAT TO EVOLVE NITROGEN AND EXPAND SAID ORGANOPLASTICMATERIAL.